Diverse Synaptic Plasticity Induced by the Interplay of Ionic Polarization and Doping at Salt-Doped Electrolyte/Semiconducting Polymer Interface

Pt/Ca2+–polyethylene oxide/polymer poly­[3-hexylthiophene-2,5-diyl]/Pt devices were fabricated, and their pulse responses were studied. The discharging peak, represented by the postsynaptic current (PSC), first increases and then decreases with increasing input number in a pulse train. The weight of the PSC decreased for low-frequency stimulations but increased for high-frequency stimulations. However, the peak of the negative differential resistance during the charging process varied following the opposite trend. These behaviors suggested the ability for transferring the signal bidirectionally, confirming the equivalence between the ionic kinetics of our device and the transmitter kinetics of one kind of synapse. A facilitation (F)–depression (D) interplay model corresponding to the ionic polarization and doping interplay at the electrolyte/semiconducting polymer interface was adopted to successfully mimic the weight modification of the PSC. The simulation results showed that the observed synaptic plasticity was caused by the great disparity between the recovery time constants of F and D (τ F and τ D ). Moreover, such an interplay could inspire the features of responses to post-tetanic stimulations. Our study suggested a means to realize synaptic computation.